This was a feature added in Notes 4.5 to enable servers to provide a single person/group directory for multiple Notes domains. However, it is a common mistake to put the standard names.nsf file in the Master Address Book field of the server document. The result is the error message above.
To correct this problem, either remove names.nsf from this field, or create a new database named mab.nsf from the mab.ntf template and put mab.nsf in this field. If you really do have NABs for multiple domains on your server, you can set up Directory Assistance as specified in the on-line help.